The production of solvent insoluble microgel particles and their use in solution coating compositions to provide sag resistance as the deposited coatings cure, usually as they are baked to provoke some thermal curing reaction, is known. This is shown in H. J. Wright et al. U.S. Pat. Nos. 4,290,932 and 4,377,661 where the microgel particles are prepared by the aqueous emulsion polymerization of a mixture of ethylenically unsaturated monomers, at least one of which is an acrylic or methacrylic acid, or an hydroxy-substituted alkyl ester thereof, another of which is an alkyl ester of an acrylic or methacrylic acid, styrene or alpha-methyl styrene, and a multifunctional cross-linking agent which is a polyethylenically unsaturated material. The microgel particles are insoluble in the organic solvent which is selected, and after removal of water the dispersion of insoluble particles in organic solvent is incorporated into a solution coating composition containing a dissolved copolymer which also contains acid or hydroxy groups and which are prepared from monomers selected in the same way indicated previously. In the issued patents, the particles of microgel solids are required to be present in an amount of from 5% to 15 % of the total resin solids.
It is desired to provide cross-linked dispersion copolymers which exhibit extensive swellability in the selected solvents, but which can be used in much the same way as the microgel particles in the prior art, and which can be made using large amounts of less costly monomers. These cross-linked dispersion copolymers are effective when introduced into solution coating compositions to enhance sag resistance even when used in smaller amounts, preferably below 3%, and more preferably below 1% of the total resin solids. It is also desired to provide organic solvent solution coating compositions which possess improved viscosity stability, whereas the coating compositions of the prior art were not stable, and increased in viscosity with time.